<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    div{
        width: 500px;
        height: 500px;
        background-color: aquamarine;
    }
</style>
<body>
    <div></div>
    <script>
        let div=document.querySelector('div');
        window.addEventListener('resize',function(){
            if(window.innerWidth<800){
                div.style.display='none';
            }else{
                div.style.display='block';
            }
        })
    </script>
</body>
</html>